netdev - Re: [RFC PATCH V3 08/11] swiotlb: Add bounce buffer remap address setting function

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Message-ID: <94038087-a33c-93c5-27bf-7ec1f6f5f0e3@arm.com>
Date:   Mon, 14 Jun 2021 14:49:51 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>, Tianyu Lan <ltykernel@...il.com>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        wei.liu@...nel.org, decui@...rosoft.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
        arnd@...db.de, dave.hansen@...ux.intel.com, luto@...nel.org,
        peterz@...radead.org, akpm@...ux-foundation.org,
        kirill.shutemov@...ux.intel.com, rppt@...nel.org,
        hannes@...xchg.org, cai@....pw, krish.sadhukhan@...cle.com,
        saravanand@...com, Tianyu.Lan@...rosoft.com,
        konrad.wilk@...cle.com, m.szyprowski@...sung.com,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        sstabellini@...nel.org, joro@...tes.org, will@...nel.org,
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        kuba@...nel.org, jejb@...ux.ibm.com, martin.petersen@...cle.com,
        iommu@...ts.linux-foundation.org, linux-arch@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, netdev@...r.kernel.org,
        vkuznets@...hat.com, thomas.lendacky@....com,
        brijesh.singh@....com, sunilmut@...rosoft.com
Subject: Re: [RFC PATCH V3 08/11] swiotlb: Add bounce buffer remap address
 setting function

On 2021-06-07 07:43, Christoph Hellwig wrote:
> On Sun, May 30, 2021 at 11:06:25AM -0400, Tianyu Lan wrote:
>> From: Tianyu Lan <Tianyu.Lan@...rosoft.com>
>>
>> For Hyper-V isolation VM with AMD SEV SNP, the bounce buffer(shared memory)
>> needs to be accessed via extra address space(e.g address above bit39).
>> Hyper-V code may remap extra address space outside of swiotlb. swiotlb_
>> bounce() needs to use remap virtual address to copy data from/to bounce
>> buffer. Add new interface swiotlb_set_bounce_remap() to do that.
> 
> Why can't you use the bus_dma_region ranges to remap to your preferred
> address?

FWIW, I think a better generalisation for this would be allowing 
set_memory_decrypted() to return an address rather than implicitly 
operating in-place, and hide all the various hypervisor hooks behind that.

Robin.